Defective interfering (DI) particles have been isolated from many virus families. The particles are defective because a portion of the viral genome is deleted and they need the assistance of the homologous standard helper virus to replicate. The particles are interfering because their replication interferes with the replication of the helper virus in a coinfection. DI particles of poliovirus have been isolated and extensively studied. With these particles, a portion of the viral genome is deleted that lies within the capsid protein region. Cells infected with poliovirus DI particles produce viral proteins but the viral capsid proteins are aberrant. We have isolated two different DI particles of encephalomyocarditis (EMC) virus, one from the wild type and temperature-sensitive EMC virus. The characterization of these particles will be with sucrose gradient centrifugation and gel electrophoresis of the purified RNA. In addition, the ability of the DI particle RNA to code for protein in infected cells will be examined. Finally, the ability of the purified DI particle RNA to function in in vitro protein synthesis will be studied. These experiments should allow us to gain a better knowledge of picornavirus genetics. The application also proposes inoculating EMC DI particles with wild type EMC virus into mice to determine if a diabetic condition is induced in the same way as the M variant of EMC is diabetogenic.